因为x^2+y^2+4x-6y+15
=x^2+4x+4+y^2-6y+9+2
=(x+2)^2+(y-3)^2+2 ,
(x+2)^2≥0,(y-3)^2≥0,
所以当x=-2,y=3时,(x+2)^2+(y-3)^2+2有最小值,最小值是2